Introduction
Tropical rainforests comprise an ecology that has the highest species diversity due to the availability of food, water, space, and sunlight. In essence, tropical rainforests have a high carrying capacity of flora and fauna when compared to ecosystems in Arctic and Antarctic regions. However, increasing habitat loss is a major challenge of tropical rainforests because it threatens the existence and survival of fauna and flora (Aparecida et al. 2015).
Although natural activities such as volcanism, climate change, and fires contribute to habitat loss in tropical rainforests, anthropogenic activities are the primary causes. Land conversion for agriculture, settlement, and infrastructure coupled with pollution has immensely contributed to the destruction of habitat in tropical rainforests (Morante-Filho et al. 2016). The existence of numerous factors that contribute to habitat loss complicates conservation efforts aimed at maintaining species richness and diversity of tropical rainforests. Therefore, the purpose of this research paper is to examine how habitat loss affects the ecology of tropical rainforest.
History of Habitat Loss
The history of habitat loss correlates with the encroachment and settlement of people in tropical rainforests. Ecologists predict that mass extinction of species would occur in tropical forests because they host a significant proportion of the Earth’s terrestrial species (Alroy 2017). Human activities have a disastrous impact on the existence and survival of species in tropical rainforests because they contribute to global warming.
According to Morante-Filho et al. (2016), global climate change has catastrophic effects on flora and fauna because it has irreversible effects. Since forests dominate the tropical ecosystems, their destruction by human activities and climate change reduces water, food, and space for flora and fauna to grow sustainably (Aparecida et al. 2015). Massive deforestation of tropical rainforests to harvest wood for construction resulted in the decline of global forest cover by 5% in 2000-2010 (Alroy 2017). The ecological implication is that habitat loss reduces species diversity, disrupts food chains, and displaces organisms in their native habitats.
Decreases Growth
Germination and Recruitment of Seedlings
Habitat loss due to human activities has a negative influence on the growth and establishment of tropical rainforests. Anthropogenic activities contribute to the loss of habitats by disrupting native environmental processes (Aparecida et al. 2015). Anthropogenic activities cause encroachment of habitats, fragmentation of ecological systems, and restriction of biotic interactions, leading to the reduced species diversity and populations in tropical forests. In the food chain, beneficial interactions between animals and plants contribute to the regeneration of vegetation and sustenance of forest cover.
When plants produce their seeds, animals aid in dispersing them to various regions in the habitat where they germinate and grow amidst the interaction of biotic and abiotic factors (Aparecida et al. 2015). The environmental condition of habitats in which seed dispersal occurs determines predation, the germination rate, and the recruitment of seedlings in tropical forests.
Keystone palm (Euterpe edulis) is an example of a tropical plant in the Brazilian Atlantic Forest affected by the loss of habitat in tropical rainforests. According to Aparecida et al. (2015), habitat loss limits the interaction of abiotic and biotic factors and consequently decreases the rate of seed germination and seedling recruitment of E. edulis.
Infestation by fungi and predation by invertebrates and vertebrates comprise biotic factors that reduce the germination rate of seeds. Forest cover forms abiotic factor because it creates a favorable environmental condition that promotes their germination and recruitment of seedlings into an established forest. Aparecida et al. (2015) report that forested areas exhibited a higher rate of germination and recruitment of seedlings than non-forested areas. These findings imply that forests protect seeds of E. edulis from predators and nurture the growth of seedlings into mature plants.
Fragments Habitats
The increasing anthropogenic activities across the world have reduced the biodiversity of tropical rainforests. Due to declining tropical reserves of rainforests, environmental agencies have instituted conservation efforts to improve biodiversity. According to Martinez-Ramos et al. (2016), defaunation and fragmentation are two anthropogenic activities that threaten the conservation of the tropical rainforests. Defaunation destroys rainforests leading to the reduction of native diversity, decline in herbivores, and the proliferation of invasive species that are tolerant to open habitats.
Fragmentation reduces species diversity by decreasing area of habitats for functional ecosystems that permit coexistence of seed dispersers, pollinators, herbivores, and predators. Synergistic impacts of deforestation and fragmentation cause long-term loss of habitats and significant reduction of biodiversity in tropical regions. In their study at Los Tuxtlas in the Americas, Martinez-Ramos et al. (2016) established that anthropogenic activities reduce biodiversity by fragmenting habitats and causing the proliferation of invasive species. Thus, the reduction of biodiversity is a significant impact of anthropogenic activities that contribute to habitat loss.
Restricts Gene Flow
Habitat loss restricts gene flow in a population because it causes fragmentation and isolation of various species in tropical rainforests. Anthropogenic activities cause fragmentation of habitats into isolated islands of populations where there is inbreeding coupled with restricted mating and constrained transfer of pollen grains, resulting in a reduced level genetic diversity.
Suarez-Montes, Chavez-Pesqueira, and Nunez-Farfan (2016) explain that habitat loss through fragmentation alters gene flow by reducing outcrossing rates, increasing inbreeding, limiting speciation, and decreasing genetic adaptation. The impact of habitat loss on tropical rainforests depends on the nature of lifespan, mating system, life history, mobility, population size genetic diversity, and genetic structure.
Habitat loss through fragmentation influences the gene flow of Aphelandra aurantiaca, which is an understory herb of rainforest in southern parts of Mexico. The analysis of the gene flow in various populations revealed that habitat fragmentation reduces species diversity (Suarez-Montes, Chavez-Pesqueira, and Nunez-Farfan 2016).
In rainforests, the pollution of A. aurantiaca depends on hummingbird, bumblebees, and butterflies. The reliance on birds and insects in pollination implies that isolation due to fragmentation limits encourages inbreeding and prevents crossbreeding between islands of the population. As an understory herb, A. aurantiaca requires forests to regulate the amount of sunlight using their canopies. In this view, the destruction of rainforests threatens the existence of A. aurantiaca in open areas exposing them to direct and intense sunlight.
Suarez-Montes, Chavez-Pesqueira, and Nunez-Farfan (2016) found out that fragmentation did not affect genetic diversity owing to large and diverse islands of the population. Moreover, efficiency pollinators reduced inbreeding for they ensured that there are cross-pollination and connection between fragmented populations.
In nature, gene flow requires the effective interaction of plants, pollinators, and seed dispersers. Habitat loss causes fragmentation of tropical rainforests, which in turn disrupts the transfer of pollen grains and the dispersion of seeds (Browne and Karubian 2018). Anthropogenic activities have reduced extensive tracts of rainforests into isolated patches and partial ecosystems with variable genetic diversity.
For ecosystems to function optimally, gene flow should not experience restrictions in the aspects of pollination and dispersion of seeds. According to Browne and Karubian (2018), habitat loss and fragmentation reduces the genetic diversity of rainforests by limiting crossbreeding and encouraging inbreeding of plants within their isolated patches. The interaction between plants, insects, and animals in tropical rainforests is dependent on the integrity of ecosystems.
A disturbed ecosystem reduces or displaces insects and animals, which play a significant role in the food chain as pollinators and dispersers of seeds. Subsequently, decimated and fragmented rainforests lack adequate pollinators and seed dispersers, leading to a declined biodiversity. A study conducted by Browne and Karubian (2018) in Ecuador established that habitat loss and fragmentation of palms, Oenocarpus bataua, reduce genetic diversity and reinforce the genetic structure. Therefore, habitat loss is a substantial factor that restricts gene flow and shrinkages genetic diversity of tropical rainforests.
Reduces Functional Diversity
Insects Herbivory
As the most diverse species in tropical rainforests is insects, habitat loss has a vast impact on their food chains, interaction, and distribution. The mechanism through which habitat loss affects the existence and survival of insects is multitrophic effects (Morante-Filho et al. 2016). Bottom-up and top-down ecological processes are two aspects of multitrophic effects of habitat loss on herbivory habits of insects.
Bottom-up ecological processes promote growth, increase species diversity, and create a robust food chain. Habitat loss trigger bottom-up processes in the ecosystems for insects starts to compete for decreasing resources, such as food, shelter, and space, leading to the depressed growth and reduced diversity due to the extinction of the unfit ones. In contrast, top-bottom ecological processes have negative impacts because they decrease the population, diversity, and food chains of insects. Changing ecological dynamics due to habitat loss could increase predation and favor certain diseases, resulting in the massive decimation of the dominant populations of insects in tropical rainforests.
The complex multitrophic effects elucidate how habitat loss in tropical rainforests influences herbivory habits of insects. In their study, Morante-Filho et al. (2016) employed multitrophic analysis on the Brazilian Atlantic rainforest and established that forest cover and structure, as well as the abundance of insect predators and herbivorous arthropods, are dependent on habitat loss. Habitat loss affects bottom-up ecological processes since it decreases forest cover and simplifies vegetation structure, leading to reduced availability of resources and space for insects.
Moreover, habitat loss upsets top-down ecological processes because it decreases the impact of predators, which are mainly birds and predatory arthropods, resulting in an increased population of insects. Morante-Filho et al. (2016) argue that forest loss in tropical regions threatens biodiversity because it undermines both bottom-up and top-down control processes of ecological systems. Consequently, destruction of habitat favors herbivorous insects but lessens the diversity of vertebrate and invertebrate predators, which rely on forest cover for shelter and food.
Foraging Behavior of Dung Beetles
Since human activities influence the vegetation cover of ecosystems, they shape ecological systems of agroforestry and foraging behavior of vertebrates and invertebrates. Santos-Heredia et al. (2018) assert that dung beetles are appropriate biotic indicators of forest disturbance since their foraging behaviors are sensitive to changes in environmental conditions. In essence, the community of dung beetle depicts the functionality of ecosystems in maintaining and sustaining its ecological processes sustainably.
The number of species, size, weight, soil excavation, seed dispersal, dung removal, and seed exhumation are some of the parameters of dung beetle used to infer integrity of rainforests. The loss of habitat usually results in the reduced foraging behavior of dung beetle, leading to poor aeration of soil and affected dispersal of seeds in tropical rainforests.
Since agrosystems constitute human activities that cause habitat loss, they have critical impacts on interaction, food chain, and distribution of dung beetles and other organisms in the environment. Santos-Heredia et al. (2018) evaluated the impact of anthropogenic activities on the community and ecological functions of dung beetle in the Lacandona rainforest region, Mexico. As a region with diverse agroforestry systems, Lacandona hosts different levels of beetle community and sustain diverse ecological processes. The dominant ecological systems in Lacandona are conserved forests, polyculture cocoa, rustic cocoa, and rubber monoculture.
These ecological systems depict different degrees of how anthropogenic activities have reduced habitat loss in tropical rainforest through agroforestry. The analysis data obtained from diverse ecological systems confirmed that anthropogenic activities reduce diversity and biomass, as well as diminish the foraging behavior of dung beetle (Santos-Heredia et al. 2018). In this view, the loss of habitat causes tropical ecosystems to lose ecological functions such as soil excavation, seed dispersal, dung removal, and seed exhumation, which are integral in the regeneration of forests.
Neotropical bats
Habitat loss reduces the functional diversity of tropical rainforests because it influences the proportions of fauna and flora in varied ecosystems, characterized by interactions, food web, and distributions. Garcia-Morales et al. (2016) explain that functional diversity provides a comprehensive assessment of tropical rainforests because it measures functions, resilience, resistance, and diversity of ecosystems. Since tropical rainforests form an ecological system, habitat loss disturbs critical ecological processes involved in the maintenance and perpetuation of biodiversity. The impact of habitat loss is evident among Neotropical bats because they comprise 50% of mammals in Hidalgo, Mexico, and their natural history, foraging behavior, flight capacities, diet, and distribution are well-known.
The examination of ecology and functional diversity of bats depicts impacts of habitat loss on rainforests. According to Garcia-Morales et al. (2016), functional diversity, abundance, and species richness have a negative relationship with the loss of habitat in tropical rainforests. These findings imply that habitat loss has a marked impact on the food chain, interaction, and distribution of bats in Hidalgo’s rainforests. As Neotropical bats play a critical role in pollination, seed dispersal, and insect predation, they influence gene flow and biodiversity of plants in tropical rainforests.
Arthropod Biodiversity
Habitat loss affects arthropod biodiversity because the fragmentation of ecosystems interferes with biotic interactions. Changes in tropical rainforests due to anthropogenic activities that lead to loss and fragmentation of ecosystems threaten the existence and survival of arthropods, as well as plants due to functional biotic interactions. The presence of biotic interactions and relationships indicate that the nature of habitat influences abundance, species richness, distribution, and diversity of plants and animals. The multitrophic analysis reveals that Heliconia aurantiaca exhibits biotic interact with herbivores, omnivores, and predators in tropical rainforests; hence, influencing their distribution and diversity in various ecosystems (Benitez-Malvido et al. 2016).
Habitat loss and fragmentation of forests disrupt this form of biotic relationships due to the decrease in the population of herbivores. Benitez-Malvido et al. (2016) established that in fragmented rainforests, H. aurantiaca demonstrated the existence of a nested structure of Heliconia-arthropod association. Hence, the findings illustrate that fragmentation of rainforests affects the relationship between arthropods, omnivores, herbivores, and plants, leading to reduced biodiversity, abundance, distribution, and species richness.
Causes Climate Change
Habitat loss has an enormous impact on climate change because it reduces vegetation cover on the Earth’s surface, increases surface air temperature, and affects purification of air. For centuries, continued habitat loss has long-term impacts on climate change since tropical rainforests act as carbon sinks that regulate global warming. An increased depletion of habitat decreases utilization of carbon dioxide and causes its accumulation in the atmosphere, which results in global warming and climate change. Longobardi et al. (2016) explain that deforestation increases the proportion of carbon dioxide in the atmosphere and alter the balance of mass and energy on the Earth’s surface, leading to changes in local and global climatic conditions.
The loss of habitat through deforestation exposes the Earth’s surface to sunlight and increase the loss of water through evaporation. Longobardi et al. (2016) assert that climate change occurs when the soil and surface air temperatures increase significantly in deforested areas. Hence, climate change has an overall impact of decimating flora and fauna, particularly the ones that are sensitive to harsh climatic conditions.
Habitat loss can cause climate change by reducing rainfall patterns, and subsequently, decreasing biotic diversity. Brawn (2017) argues that large-scale loss of habitat due to agricultural activities changes precipitation patterns to seasonal and xeric conditions, which threaten the existence of tropical ecosystems. Reduced levels and seasonal variations of precipitations in deforested and agricultural areas affect rainforest ecosystems and threaten the survival of less tolerant fauna and flora.
Brawn (2017) elucidates that habitat loss affects precipitation patterns and causes selective survival and reproduction of fauna, and thus, trigger cascading effects in ecosystems that upset interaction, distribution, and food chain of organisms. Therefore, the loss of habitat due to anthropogenic activities such as deforestation and land use contribute to reduced precipitation and loss of species in tropical rainforests.
Potential Solutions
- To improve gene flow in the fragmented tropical rain forests, conservation strategies should consider that population size, genetic structure, and life history are necessary to create viable populations with evolutionary potential (Suarez-Montes, Chavez-Pesqueira, and Nunez-Farfan 2016; Browne and Karubian 2018).
- Conservation of pollinators and seed dispersers is essential to enhance the diversity of plants in tropical rainforests, as well as animals that rely on this ecosystem (Browne and Karubian 2018; Benitez-Malvido et al. 2016).
- Prevention of climate change due to habitat loss requires afforestation to lower surface temperatures and increase the precipitation, and the use of precipitation refugia to conserve and maintain biodiversity in cases of extreme climate changes (Brawn 2017; Longobardi et al. 2016).
- Improve ecological processes and maintain functional biodiversity of tropical rainforests because plant, animals, and environment have intricate relationships that allow them to undergo self-regulation through bottom-up and top-down mechanisms (Morante-Filho et al. 2016; Morante-Filho et al. 2016; Santos-Heredia et al. 2018; Garcia-Morales et al. 2016; Benitez-Malvido et al. 2016).
Conclusion and Directions for Future Research
History indicates that habitat loss has an enormous impact on tropical rainforests because it reduces biodiversity significantly. The analysis of literature revealed that significant impacts associated with habitat loss are decreased growth of fauna and flora, restricted gene flow, reduced functional diversity, and climate change. As broader implications, these impacts demonstrate that habitat loss is a significant threat of biodiversity and requires urgent conservation measures to avert a massive environmental crisis. Moreover, since these impacts emanate from studies performed in few sites with tropical rainforests, further research is necessary to replicate them in various regions across the world (Benitez-Malvido et al. 2016).
Moreover, supplementary studies are essential to establish how local conditions mediate the impact of habitat loss on tropical rainforests (Benitez-Malvido et al. 2016; Longobardi et al. 2016). Overall, further research would generate additional information and enhance the internal and external validity of the current findings.
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